Many processes require an extraction step in recovering the desired product. In some extraction processes undesirable impurities may be removed from a fluid system while in other extraction processes the product may be removed from the fluid system. Common extraction involves placing a fluid containing the component to be extracted (the extractive component) in direct contact, usually by rapid mixing, with a second fluid (the extraction fluid) which attracts or traps the extractive component, thereby reducing the level of that component in the first fluid. Unfortunately, extraction by conventional methods many times leaves entrained phases of the extraction fluid in the fluid which is being acted upon. These entrained phases contain the very components which are meant to be extracted from the first fluid. As an example, polymerization and hydrogenation of polymer cements requires the use of polymerization initiators and hydrogenation catalyst. Extraction of the initiator and/or catalyst is required to produce a polymer relatively free of metals found in the initiator and/or catalyst. Conventional methods of extraction are to either disperse acids, such as sulfuric or phosphoric acid, into the polymer cement, or to disperse polymer cement into acids, both methods commonly accomplished by rapid mixing for a period of time, followed by allowing the material to settle and separate. Extraction by this conventional method leaves entrained acid phases in the polymer cement. Metal impurities successfully extracted to the acid are thereby returned to and entrapped in the cement when the acid becomes entrained. Further, trapped acid phases reduce extraction efficiency and leave residuals of the acid, such as sulfates or phosphates, in the final polymer product.
Another problem with conventional extraction is that the rapid mixing commonly leads to a "rag layer" upon settling. The rag layer is an emulsification of the first and second fluids that will not separate and has no commercial use; it is a waste of an amount of the desired first fluid. Therefore, it would be desirable to have an extraction technology that achieves high extraction efficiency without leaving other residuals in the final product and which reduces or eliminates wasteful rag layer.
It has surprisingly been found that reduction of the level of mechanical agitation during extraction allows for short-time extraction with substantially no residual contaminates or rag layers. In many instances, total extraction times are reduced from those of conventional methods.